Simple Temperature Controller

This temperature controller employs an LM135/235/335 temperature sensor, can be used to keep small environment warm or hot. Here is the schematic diagram:

LM311 is used as comparator, to detect if the voltage at sensor pin (the inverting input) goes higher than the reference pin (the non-inverting pin). If this condition is detected, the comparator will switch off the heater driver (BUV26). Practically, after the desired temperature is met, the heater will be oscillating on-off, trying to keep the voltages at non-inverting input and inverting input equal. [Source: STMicroelectronics Application Note]